Field of the Invention
The present invention relates to an interaction arrangement for interaction between at least one screen located behind a transparent pane and at least one pointer object located in front of the pane, comprising at least two cameras arranged behind the pane whose optical axes are oriented substantially perpendicular to the pane, wherein there is associated with each of the cameras a deflection unit via which an optical path from an interaction area in the vicinity of and in front of the pane can be directed into the camera, and comprising a computing unit connected to all of the cameras for determining a position of the pointer object which is guided so as to be visible for at least two of the cameras.
Description of the Background Art
Interactive screens are known under the name of touchscreen, in which a user moves a pointer object, for example his finger, on the screen. A position or movement of the pointer object on the screen is detected by mechanical sensors. A predefined action is triggered as a function of the position or other actions of the pointer object, for example, by pressing on a certain area of the screen. Such systems are subject to mechanical wear resulting from vandalism and scratching, and because of the resultant high maintenance costs are only suitable for long-term use under certain conditions, for example in public areas.
Consequently, systems have been developed that determine the position of the pointer object with respect to a passive surface by optical detection. U.S. Pat. No. 7,034,807 discloses an arrangement for interaction by a user with a screen through a display window. The area of the screen visible through the display window serves as a passive touch surface. The system comprises a recording unit for recording the pointer object in the vicinity of the touch surface with optical means. A computing unit connected to the recording unit can calculate a position of the pointer object in the vicinity of the contact surface from the signals recorded by the recording unit. The screen is located behind the display window, which to say that it is separated from the user by the display window. The recording unit comprises, for example, two cameras, and is also located behind the display window. By means of a deflection unit, for example mirrors or prisms, located above or below the contact surface, an optical path is directed from the recording unit to an area in front of the contact surface. In order to increase the contrast, the area in front of the contact surface is illuminated with infrared light that has the same optical path as the recording unit. Reflecting surfaces are arranged opposite the deflection unit with respect to the contact surface. They reflect the infrared light and serve as a background before which the pointer object can be detected with increased contrast. The position of the pointer object can then be determined, for example by triangulation.
Similar camera-based interactive systems are disclosed in WO 02/03316 A1, EP 1420335 A1, which corresponds to U.S. Pat. No. 6,954,197 and DE 10163648 A1, for example. These documents teach the use of a recording unit with at least two cameras with overlapping fields of view that include a contact surface delimited by a frame. The presence of a pointer object on or in the vicinity of the contact surface is detected by analysis of the differences between two successive images of the contact surface. When a pointer object is present, the recorded image data are processed such that only selected subareas of the image are analyzed.
Conventional camera-based interactive systems have the inherent problem that the images recorded by the recording unit are frequently distorted by light from other sources, for example directly incident, scattered, or reflected light from the surroundings. Light from such external sources often has a higher intensity than light coming from the pointer object. Since the camera controller generally adjusts itself for the maximum intensity, detection of the pointer object frequently becomes difficult or impossible. Moreover, the recorded image is frequently very sensitive to changes in ambient light, for example between day and night. These circumstances lead to errors in determining the position of the pointer object.
Additional infrared illumination for illuminating the area in front of the contact surface can be used together with corresponding infrared-sensitive cameras to reduce these errors. Contrast can be further improved by means of the aforementioned reflecting surfaces. The illuminated pointer object can then be detected with higher contrast. However, this makes the system more complex and costly.
Another problem arises with double-glazed display windows between the user and screen. Light can be reflected between the window panes, reach the recording unit, and distort the recorded image, thus making it difficult or impossible to determine the position of the pointer object.